1. Field of the Invention
The present invention relates to a video signal processing apparatus for processing video signals.
2. Related Background Art
Hitherto, as a method of switching a plurality of kinds of video images on screen, there has been known an apparatus for switching video images by a special effects such as wipe or fade.
On the other hand, in recent years, in an apparatus in which a video camera and a recording apparatus are integral, an apparatus having a video image editing function such as wipe, fade, or the like as mentioned above has been put into practical use.
However, the apparatus as mentioned above has, for instance, a memory circuit. An arbitrary still image is previously stored in the memory circuit, a video signal corresponding to the still image stored in the memory circuit and a video signal corresponding to an object image which is formed by a video camera unit are switched by sequentially changing switching timings or mixed by sequentially changing a mixture ratio, and the resultant switched or mixed signal is output, thereby accomplishing a special effect such as wipe or fade.
During the execution of the above special effect, a state of the special effect is displayed on an electric view finder (EVF) of the apparatus. However, at the start of the special effect, a still image stored in the memory circuit in the apparatus is displayed on the EVF. The image corresponding to the video signal which is formed by the video camera unit cannot be monitored by the EVF and the using efficiency is low.
On the other hand, hitherto, as one of special functions which the video camera has, there is a fading function such that the video signal obtained from an image pickup device is gradually erased and the whole picture plane is set to the white or black level, or on the contrary, the video signal is gradually mixed with the white or black picture plane.
FIG. 1 is a constructional diagram showing a construction of a conventional image pickup apparatus. In FIG. 1, reference numeral 1 denotes an image pickup device to convert a video image which was input through a lens into a video signal; 2 indicates a sample and hold (S/H) circuit to sample and hold the video signal which was output from the image pickup device 1; 3 is an auto gain control (AGC) circuit to execute an automatic gain control process, a gamma process, and the like on the video signal which is output from the S/H circuit 2; 4 is a multiplexing circuit to multiplex a synchronizing (or sync) signal with the video signal; 5 is a fading circuit to execute the fading operation; 6 is a driving circuit to generate a drive pulse to drive the image pickup device 1; 7 is a synchronism signal generating circuit to generate a sync signal, clamp pulse, and the like; 9 is a time constant circuit to provide a time constant so that a video image gradually changes upon fading; 10 is a switch to activate the start of the fading operation; 11 is a recording unit with record the video signal to which the sync signal was multiplexed and which is output from the multiplexing circuit 4; and 12 is an electric view finder (EVF) unit to display the video signal which is output from the multiplexing circuit 4.
The operation of the apparatus shown in FIG. 1 will now be described hereinbelow.
First, the video signal obtained from the image pickup device 1 is sampled and held by the S/H circuit 2 and, thereafter, is subjected to the AGC and gamma processes by the AGC circuit 3 and the processed signal is input to the fading circuit 5. By turning on the switch 10, the fading circuit 5 makes the fading function operative in accordance with a fade control signal which is output from the time constant circuit 9, thereby executing the fading process on the video signal. The fading-processed video signal is supplied to the multiplexing circuit 4. After that, the sync signal is multiplexed with the faded video signal by the multiplexing circuit 4 and the multiplexed signal is output to the recording unit 11 and also supplied to the EVF unit 12. The photographed video image can be confirmed by the EVF unit 12 during the photographing and recording in the recording unit 11.
As mentioned above, in the conventional apparatus, in the case where the fading function is made operative, the video signal which is input to the EVF unit 12 has already been fading-processed by the fading circuit 5, so that the picture plane in the EVF unit 12 is set to a whole white or black image in accordance with the fade control signal. Therefore, in the fading state, the photographer cannot check the video image which is output from the image pickup device 1. Particularly, in the case where the video signal is gradually mixed from the fading state in which the picture plane is set to a whole white or black image and the photographing and recording operations are started (at the time of fade-in), the video image in which the photographing and recording operations are started cannot be checked. Thus, there is a problem such that the fading function cannot be effectively used because the photographing and recording operations are started with a video image different from an image desired by the photographer.